I just stumbled upon a game project that is meant to produce a real-time strategy game in a historical setting. There will be slingers in it. Balearic Slingers are mentioned to have been used by Carthagians, and later by Romans. However, they also mention them being Iberians at the Iberian page, although that has been commented upon.
There is little to read about their slingers, but the concept picture of three levels of slingers is quite interesting. Other units increase in equipment, like Roman Velites getting first another spear to throw, then proper throwing spears, and armor also getting better. I also think they would increase in skill. Anyway, the only concept picture of slingers shows them getting additional slings of different lengths...
There isn't any other different between the levels of slingers, as they don't wear armor and the better ones aren't any richer...
I don't know how complete the project is, but the screenshots already show battles. If those screenshots are straight from the game, it will be one heck of a freeware RTS. With Balearic Slingers who outrange Archers a long way.